Adjustable tap means for variable resistance device



1959 P. c. SMITH 2,

ADJUSTABLE TAP MEANS FOR VARIABLE RESISTANCE DEVICE Filed Jan. 23, 1956I r K 4 i 40 26 I6 I 427%; 44 22 Q r ,M Q

Fig. 4

INVENTOR.

' Paul O. Smith AGENT.

United States Patent ADJUSTABLE TAP MEANS FOR VARIABLE RESISTANCE DEVICEPaul C. Smith, Far Rockaway, N.Y., assignor to Micro MachineWorks, Inc.,a corporation of New York Application January 23, 1956, Serial No.560,729 3 Claims. 01. 338-135) with respect to the associated resistancewinding and additionally, similar taps of similar potentiometers must beindividually set to compensate for unavoidable differences in thevarious resistors. To obviate these inaccuracies, it is necessary thatthese taps are individually adjustable during the assembly of thepotentiometer and capable of retaining this setting when being locked inplace.

At the present time, it is the practice to form a tap of a spring striphaving a slotted ear, the slot having a screw passing therethrough andclamping the ear to a non-conductive element to lock the tap in place.It has been found, that with the most accurate setting of the tap, whenthe locking screw is tightened, it is impossible to prevent the tap frommoving slightly. Additionally, because of the width of the tap arm andthe extending ears of the standard type taps, it is impossible to groupmore than two taps in close proximity to one another.

Therefore, it is an object of this invention to provide wire-form tapsfor potentiometers which are easily and positively adjustable withrespect to the associated resistance winding and adaptable to retain theprecise setting while being locked in position.

Another object of this invention is to provide a wireform tap contactfor variable resistance units which are not deformed during adjustmentrelative the associated resistance winding which may remain in a sprungcondition until after being locked in the desired position.

Still another object of this invention is to provide formed wire tapsfor precision type potentiometers which may be ganged in close proximityto one another and not being limited in number due to the physicalcharac= teristics of the taps.

These and other objects and advantages will become more apparent byreference to the following description and the accompanying drawingswherein:

Figure 1 is a plan view of a variable resistor or potentiometer with therotor element removed and incorporating the present invention,

Figure 2 is a sectional view of a potentiometer taken on line 22 ofFigure 1,

Figure 3 is an enlarged view of the tap contact, and

Figure 4 is an end view of the tap contact taken on the plane 4-4 ofFigure 3 and indicating the path of the tap contact point as the tap ispivotally positioned. Now referring to the drawings, the potentiometerhas 2,901,719 C6 Patented Aug. 25, 1959 a cylindrical shell or case 10which is normally metallic and fixed thereto is a terminal board 12which mounts the terminals 14. These terminals 14 are electricallyjoined to the commutator (not shown) and the various taps or tapcontacts 32 by lead wires 16. Lining the shell 10 is an insulation 18,in this instance, being com prised of a synthetic, non-conductive ringor coil form 20 and a flanged, cup-shaped member or tap disc 22 which isalso made of a non-conductive synthetic. This insulation, lining theshell, not only segregates the electrical components within thepotentiometer but also is the mounting stmcture for the taps 32, theresistance coil winding 40 and the commutator (not shown). Whensynthetic material is used, the two piece construction of the insulation18 is preferred inasmuch as closer tolerances can be held to a greaterdegree than if the insulat-. ing member is formed in a single unit. Itshould be understood, that while this is merely a preferred form, thisdoes not preclude the use of a single unit construction of theinsulating member. The tap disc 22 has a hub portion 26 which surroundsthe enlarged portion of the shell 10 which mounts a rotor assembly (notshown) and is spaced therefrom to provide a circular passageway for thelead wires 16. Although the path of the lead wires is not critical, thewires are coursed through the provided passageway within the hub portion26 instead of around the outside of the hub to pervent fouling and as anadded precaution against shorting. There is a slot 28 in the flangeportion 24 of the tap disc 22 which extends through the base of the wallof the hub portion to provide an access for the lead wires to permittheir entrance into the passageway within the hub where they attach tothe individual tap contacts. This slot 28 is located directly opposite abridge 44 through which the lead wires pass as they enter the confinesof the potentiometer. The bridge 44 serves as a track for carrying aresistance coil contact (not shown) which is carried by and forms a partof a rotor assembly (not shown) over the breach between the ends of theresistance coil 49 which is wound on a winding card 42. A series ofsmall holes or openings 30 are located in the wall of the hub 26 formounting the tap contacts 32. It is Well to note, that although the hubportion 26 is shown as being of a cylindrical, inverted cup shape withan opening in the end wall thereof, this portion could also be merely anupstanding cylindrical flange.

Each of the taps 32 (see particularly Figures 3 and 4) has a body ofmounting portion 34 which extends through a hole or opening 30 in thewall of the hub 26 on the axis AA and a spring arm portion 36 on an axisBB, the axes AA and BB forming an external angle x which is variable asto degree and as the extent of the angle increases, the possibleadjustment sweep of the tap increases. At the free end of the spring arm36 is a contact portion 38 which electrically engages the side face ofthe resistance coil 40. These taps 32 are preferably made of a preciousmetal wire and treated so as to have a degree of resiliency. Thiswire-form tap 32, in being set relative to the resistance winding 40,pivots about the axis AA, the contact point 38 traveling in an arcuatepath C which crosses successive windings of the resistance coil, as maybe seen in Figure 4. When the tap 32 is set at the desired location, thespring tension of the arm 36 will hold the contact portion 38 firmlyagainst the resistance winding 40 and the application of a small amountof a homogeneous adhesive 46 at the point where the tap 32 emerges fromthe hub portion 26 of the tap disc 22 will positively lock the tap inthe desired setting. As an alternate method of locking these taps inplace, the contact portion 38 may be joined to the resistance winding 40by the application of silver solder or any of the other acceptablematerials.

In addition to utilizing this tap construction and installation forintermediate contacts, because of the ease and accuracy of installing,they have been found more suitable for resistance coil terminal contactsthan those in use at the present time.

Having thus described my invention in the preferred form, I claim:

1. A Wire-wound variable electrical resistance unit that comprises, acylindrical casing, a non-conductive liner mounted within said casingand consisting of a circular bottom piece, an upright central hubportion and, an upright cylindrical wall portion adapted to be receivedagainst the inner Wall of said casing, said hub portion and wall portionbeing spaced from each other to define an annular cavity therebetweenand closed across one end by said circular bottom piece, a wire-woundresistance element mounted within said annular cavity against theupright cylindrical Wall and extending around substantially the entirecircumference of said wall, said central hub portion being adapted to beundercut adjacent said bottom piece at any point around its peripherysuch as to define tap element mounting means, at least one such tapelement mounting means, at least one pretensioned resilient wire tapelement having a pivot arm pivotally mounted within said mounting meansfor adjustable movement with respect to said wire-wound resistanceelement and having a contact arm adapted to engage the wire-woundresistance element in pressure relationship when the pivot arm thereofis inserted within said undercut mounting means, and means forconnecting said wire tap element into an electrical circuit exteriorlyof said casing.

2. The wire-wound variable electrical resistance unit as claimed inclaim 1, that further comprises means for forming a semi-permanent bondbetween the pivot arm of said wire tap element and said tap elementmounting means after said contact arm has been positioned at apredetermined point on the wire-wound resistance element.

3. The wire-wound variable electrical resistance unit as claimed inclaim 2, that further comprises means for forming a semi-permanent bondbetween the contact arm of said wire tap element and said wire-Woundresistance element.

References Cited in the file of this patent UNITED STATES PATENTS1,783,542 Merle Dec. 2, 1930 2,448,783 De Giers et -al. Sept. 7, 19482,551,989 Wilson May 8, 1951 2,619,570 Takats Nov. 25, 1952 2,782,288Weld Feb. 19, 1957 2,806,928 Woods et al. Sept. 17, 1957

